Existing transmissions used in tracked vehicles, such as army tanks, are designed basically for use with diesel engines. They are low speed devices typically employing hydraulic torque converters to provide the required starting characteristics and damping during mechanical gear shifting. When used as a power system in conjunction with a gas turbine engine, they do not take advantage of the torque and variable speed characteristics of the free power turbine usually present in such engines nor are they compatible with the high speed output of such free power turbines. As a result, prior art devices, in addition to being needlessly large and heavy, are not suitable for use in vehicles driven by gas turbine engines. The present invention provides an integrated power system not only capable of taking full advantage of the operating characteristics of an associated gas turbine engine but also of controlling vehicle operation with minimum intervention by its operator.